1. Field of the Invention
The present invention generally relates to radio receivers including a selective call receiver and a mobile terminal and, in particular, to a radio receiver having an analog-to-digital (A-D) converter which is used to convert a received signal from analog to digital.
2. Description of the Related Art
A selective call receiver has been widely used for various purposes and, especially, a small-sized and lightweight selective call receiver, or a pager, is suitable for being taken on the road. A basic function of the selective call receiver is to indicate by beep sound, vibration, or light the incoming call and then to inform the user of a received message, for example, displaying the received message on a liquid-crystal display (LCD) according to user's key operations.
In general, the selective call receiver is provided with several keys for inputting user's instructions such as stopping a beep, selecting a message, and deleting the message. Such a key is formed with, for example, a push button or a slide switch.
It is also known that a touch-sensitive pad, a touch-sensitive panel, or a touch-sensitive screen is widely used to determine the location of a touch on a display. Therefore, such a touch-sensitive pointing device may be used as an input device of the selective call receiver instead of the above operation keys.
In view of a selective call receiver, the touch-sensitive pointing device preferably employs the simplest structure having a pair of transparent electrodes so as to sense the X-Y location of a touch, and a voltage is alternately applied to X and Y sensing lines. The X-Y sense output voltages of the touch-sensitive pointing device are digitized by an A-D converter and the digital output signal is used to determine the location of a touch by a touch location detector.
However, the touch sensing operation and the A-D conversion of the touch-sensitive pointing device cause noises which adversely affect not only the receiving sensitivity but also the quality of received signals.
Further, in addition to an A-D converter for received signals, another A-D converter for the touch sense signal is needed, which results in increased necessary space and power consumption.